Adding more field and row validation options, error handlers

[coveralls]

Pull Request Test Coverage Report for Build 276

• 92 of 101 (91.09%) changed or added relevant lines in 8 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.7%) to 80.338%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
dataflows/processors/validate.py	45	47	95.74%
dataflows/helpers/iterable_loader.py	21	28	75.0%
<!--	Total:	92	101	91.09%	-->

Totals
Change from base Build 273:	0.7%
Covered Lines:	1426
Relevant Lines:	1775

---

💛 - Coveralls